The Roseburg Urban Sanitary Authority (RUSA) operates an innovative deammonification wetland capable of treating 5,000 gallons per day, of biosolids filtrate that has an ammonia-N concentration averaging nearly 1,000 mg/L. Liquid from solids dewatering can go either to irrigation or deammonification. The purpose of the wetland is to remove ammonia-nitrogen during periods in the spring when irrigation is not feasible. It is the first commercial zeolite-anammox system.
Biosolids generated at RUSA’s WWTP are dewatered in a center screw press Monday-Friday, year-round. The filtrate from this screw press flows to an off-line clarifier and then is batch-loaded to two wetland cells by siphons. Wetland media is clinoptilolite (a zeolite). Beds drain by siphons to a recirculation basin where a pump transfers wetland effluent to the dosing siphons. Beds flood and drain excess water is pumped back to the plant’s aeration basins.
The wetland started in November 2016 and this presentation will focus on discussing the 4 years of operational experience as well as lessons learned. After a year of complete nitrification, the wetland converted to deammonification (anammox). Since then it has averaged 53 percent deammonification, significantly reduced the ammonia recycle load on the WWTP. Performance has been highly consistent in the past three years. Adding alkalinity to maintain pH above 7.0 while in the nitrification phase was crucial to establish deammonification. Once deammonification started, alkalinity demand stopped. However, recent analysis of performance indicates that maintaining a consistent operational pH of 7.5 to 8.0 – which is ideal - may require occasional alkalinity addition.
This technology is simple and non-proprietary and has potential broad application for small to medium size wastewater systems. Flood and drain contact beds were first used in the 1890s. Anammox was first observed in a contact bed in 1902. Recirculation in flood and drain beds is also public domain technology. With careful attention to design loading criteria, construction detail including the zeolite source, and alkalinity addition during the first nitrification phase; this technology is available to utilities to manage recycle streams with high levels of ammonia-N.